FIA vice-president Mohammed Ben Sulayem pictured in a Renault F1 car at the Dubai autodrome in April, shortly before he drove it into a wall. Photograph: Frederic Lefloch/Reuters

As Flavio Briatore today considered legal action over his de facto life ban from motor sport, it emerged that his fate had been sealed by a whistleblower from his Renault team codenamed "Witness X". The witness, who was not part of the conspiracy to stage a crash at the 2008 Singapore grand prix, came to light during Renault's internal investigation. The FIA became aware of his existence last Thursday, when Renault supplied additional documents.

After being granted anonymity – only the FIA president, Max Mosley, and the body's legal advisers know his name – Witness X was interviewed by a member of the FIA's external counsel. Renault then made a third and final set of written submissions on Saturday, which said: "Renault F1 has concluded that the following had knowledge of the conspiracy to cause a safety car: Nelson Piquet Jr, Pat Symonds [the then head of engineering], Flavio Briatore and Witness X.

"Witness X was told of the idea suggested by Nelson Piquet Jr by Mr Symonds, whilst in the presence of Mr Briatore. Witness X objected to the idea. He did not know the plan was to be carried into effect until the crash happened. As a result of the evidence, including Mr Piquet's admission, Mr Symonds' responses and Witness X's evidence, Renault F1 concluded that they and Mr Briatore must have known about the conspiracy."

Mohammed Ben Sulayem, the United Arab Emirates' automobile club president and an FIA vice-president, gave further insight into the World Motor Sport Council's decision to give Renault only a suspended ban. Speaking to his local newspaper, The National, Ben Sulayem said: "We did our negotiations before and everybody is happy with the result. The verdict is fair and everyone is a winner."

Apart from appearing to suggest the matter had been settled before the court sat yesterday, Ben Sulayem also hints that wider considerations than Briatore's role in fixing last year's Singapore race played a part. "I had to be loyal to my country as well as motor sport," said Ben Sulayem, whose country hosts its first grand prix on 1 November. "Protecting the investments Abu Dhabi has made into Formula One is my duty; it is a big show and it needs teams. We all want to see Renault [in Formula One]. This is the result everyone wanted."

Piquet, who was sacked by Renault in August, was offered immunity ahead of the FIA hearing. He has said that the idea to crash was proposed to him by Symonds, in Briatore's presence.

In a letter to the members of the WMSC before the hearing, Symonds wrote: "The idea for this incident was entirely conceived by Nelson Piquet Jr. It was he who first approached me with the idea. At the time I naively believed that it was something he wanted to do for the good of the team. I was not aware of the position of his contract negotiations although with the benefit of hindsight I now consider that he believed his actions would have a favourable effect on these negotiations."

Symonds said he had not expected Piquet to crash in "a reckless fashion" but admitted: "I was the one who, when the idea was first suggested to me by Nelson Piquet Jr, should have dismissed it immediately. It is to my eternal regret and shame I did not do so. I can only say I did it out of a misguided devotion to my team and not for any personal gain whatsoever. I consider the role I have played in bringing the team to where it is today to be my life's work. In a single action I have destroyed the high reputation I have built up during a 33-year career in motor sport.

"On that night in Singapore last year I made a mistake the consequences of which I could never have imagined at the time. For that mistake I can only offer all of you, and all those touched by the action I was involved in, my profound apology."

Briatore has said he wants to prove his innocence and win compensation for damage to his image. "I am distraught," the 59-year-old Italian was quoted as saying by Gazzetta dello Sport.

Carlos Gracia, head of the Spanish motor sport federation and a member of the WMSC, said of Briatore's punishment: "It seems to me excessive. There was no clear proof against him and he was not able to defend himself either." "Moreover, I wouldn't rule out him going to ordinary justice because he has been left without his means of earning a living."

The sports lawyer Stephen Hornsby, a partner at Davenport Lyons, said: "All lifetime bans in sport are difficult. Under EU law, bans have to be proportionate. [Briatore] will argue a lifetime ban is not."